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Derivation of Field Values in Slices and Iso-surfaces

The following discussion assumes the “Source Zone” is a volume zone (IJK, FE-Tetra, FE-Brick or polyhedral). For the most part the type of volume zone does not matter with one exception dealing with polyhedral source zones (see below).

The manner for which data values are calculated for slices (or iso-surfaces) does however depend on the following:

  1. Value location for variables in the source zone
  2. Surface Generation Method (option in the “Other” tab of the slice details dialog)
  3. Slice style settings

In all cases slices will be constructed with nodes spatially located at the intersections of the slicing plane with the cell edges from the source volume zone.

With some exceptions (see discussion of Polyhedral Data below) non-spatial field values are calculated as follows:

  • If the field variable is cell centered in the source zone and the style being plotted requires the use of a cell centered value then that variable in the generated slice will be cell centered and values from source cells are transferred directly to cells in the slice. Note that if other style in the slice requires the use of nodal values then those nodal values will be derived by interpolating using the surrounding cell centered values in the slice. This derivation depends on the “Variable Derivation” setting in the Options/Performance dialog. See online help for more information.
  • If the field variable is nodal in the source zone then the resulting slice will be generated with node located values for all other variables employed by the slice. These values are generated by and linearly interpolated along the edge of the volume cell from the source zone. If primary value flooding is performed in the slice it will render the color of the entire cell based on the value of the lowest indexed nodal value in the cell.

Polyhedral Data:

If the source zone is polyhedral and the surface generation method is “All Triangles” or “Allow Quads” then the rules above “apply” with one twist, that being an artificial node is introduced into each polyhedral element in the source zone prior to further processing. This interior node is equivalent to a cell centered value. The addition of this node essentially creates many sub-elements within a given source element. From this point on the rules presented above apply with each of the sub-elements.